(A) Field of the Invention
The present disclosure relates to a semiconductor device, and more particularly, to a semiconductor device with an epitaxy layer having a substantially single crystal orientation on a patterned substrate to reduce defect density and increase protection from electrostatic discharge (ESD).
(B) Description of the Related Art
Semiconductor devices such as light-emitting diodes (LED) have been widely used in traffic lights, vehicle electronics, LCD backing lights, and general illumination. In the light-emitting diode an n-type semiconductor layer, a light-emitting region and a p-type semiconductor layer are essentially made to grow on a substrate to form a layered structure, and the electrodes are formed on the p-type semiconductor layer and on the n-type semiconductor layer. Light is generated through the recombination of holes and electrons that have been injected through the semiconductor layers to the light-emitting region, and the light is then emitted through a light transmitting electrode on the p-type semiconductor layer or from the substrate. The material used for preparing the visible light-emitting diode includes the III-V compound such as AlGaInP for green, yellow, orange or red light-emitting diodes, and GaN for blue or ultraviolet light-emitting diodes, wherein the GaN light-emitting diode is formed on the sapphire substrate. However, in the conventional light emitting diode there is a relatively high degree of lattice mismatch between the sapphire substrate and the gallium nitride layer formed on the sapphire substrate, and it is difficult to make a breakthrough in reducing dislocation density of the active layer.
Taiwanese Patent Publication No. 561632 discloses a light-emitting device with high external quantum efficiency. To stably secure high external quantum efficiency in the light emitting device, at least one recess and/or protruding portion is created for scattering or diffracting light generated in a light emitting region on the surface portion of a substrate. The recess and/or protruding portion has a shape that prevents crystal defects from occurring in semiconductor layers.
Taiwanese Patent Publication No. I236773 discloses a light emitting device including a substrate having a patterned surface and formed with a plurality of spaced apart cavities, and an epitaxial layer formed on the patterned surface of the substrate, having a patterned surface that is in contact with the patterned surface of the substrate, and formed with a plurality of protrusions that protrude from the patterned surface of the epitaxial layer and that are respectively received in the cavities. Each of the protrusions is polygonal in shape and defines a plurality of vertices. The vertices of each of the protrusions contact the cavity-defining wall of the respective one of the cavities so as to form a plurality of closed pores between each of the protrusions and the cavity-defining wall of the respective one of the cavities.
Taiwanese Patent Publication No. I253771 discloses a light emitting diode structure comprising a substrate with a surface and a plurality of cylindrical optical crystals, a first type doping semiconductor layer, a first electrode, a light emitting layer, a second type doping semiconductor layer and a second electrode. The first type doping semiconductor layer is formed on the substrate to cover the plurality of optical crystals. The light emitting layer, the second type doping semiconductor layer and the second electrode are formed on a portion of the first type doping semiconductor layer in sequence. The first electrode is formed on the other portion of the first type doping semiconductor layer without being covered by the light emitting layer. The substrate with optical crystals can improve the epitaxial quality of the first type doping semiconductor layer and increase the energy of the light orthogonally emitting out of the light emitting diode structure, so as to sufficiently enhance the light emitting efficiency of the light emitting diode structure.
Wuu et al. discloses a near-ultraviolet nitride-based light-emitting diode (LED) with peak emission wavelengths around 410 nm (“Enhanced Output Power of Near-Ultraviolet InGaN—GaN LEDs Grown on Patterned Sapphire Substrates,” IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 17, NO. 2, FEBRUARY 2005. It was found that the electroluminescence intensity of the Patterned Sapphire Substrates (PSS) LED was 63% larger than that of the conventional LED. For a typical lamp-form PSS LED operating at a forward current of 20 mA, the output power and external quantum efficiency were estimated to be 10.4 mW and 14.1%, respectively. The improvement in the light intensity could be attributed to the decrease of threading dislocations and the increase of light extraction efficiency in the horizontal direction using a PSS.